An example of the water gate driven by the hydraulic cylinder is a tumble gate system provided across a river. Such a tumble gate system is provided for effectively utilizing river water resources by controlling the degree of tumbling of the gate provided across the river, for preventing sea water from being mixed with fresh water at the mouth of a river, or for protection against the tide at the seaside.
A tumble gate system for effectively utilizing water resources is structured such that, piers are formed at the respective sides of the tumble gate provided across the river, in each of these piers a shaft to which the tumble gate is fixed and a cum which is fixed to the shaft and is rotatable by a hydraulic cylinder are provided, and the degree of tumbling is controlled by the shaft of the cum which is rotated by the hydraulic cylinder and provided in each pier.
A reciprocating hydraulic cylinder drive circuit which functions as the driving source of the tumble gate is divided by a hydraulic cylinder, and hydraulic oil required for moving the hydraulic cylinder (i.e., the amount of which is equivalent to the capacity of the hydraulic cylinder) reciprocates in the circuit. For this reason, the hydraulic oil in the drive circuit and the hydraulic cylinder is stagnant. On this account, after long use, garbage entering the drive circuit and the hydraulic cylinder and air entering through a seal portion of the hydraulic cylinder may explode in the hydraulic cylinder due to adiabatic compression, with the result that the hydraulic oil may be contaminated by cinders of the sealing or the like.
The hydraulic oil contaminated in this way must be flushed out to prevent the occurrence of functional disorder of the hydraulic cylinder and its controller. In this regard, in the hydraulic cylinder drive circuit, the hydraulic oil in the drive circuit merely moves in accordance with the operation of the hydraulic cylinder, and it is therefore difficult to flush out contaminated hydraulic oil. Focusing on this problem, Patent Literature 1 recites that, a hydraulic oil supply circuit for supplying hydraulic oil to a hydraulic cylinder and a hydraulic oil discharge circuit are provided as shown in FIG. 7, and flushing is carried out in such a way that pressurized hydraulic oil discharged from a hydraulic pump is supplied from the hydraulic oil supply circuit to the hydraulic oil discharge circuit via the hydraulic cylinder and then returns the tank.
Now, the details of Patent Literature 1 will be given with reference to FIG. 7. As shown in FIG. 7, the hydraulic cylinder 100 is a ram cylinder, and this hydraulic cylinder 100 is structured such that a ram 102 is inserted into a cylinder main body 101 and the cylinder main body 101 and the ram 102 constitute a pressure chamber 103 penetrated by a port 104 and a port 105. The port 104 is connected to the hydraulic oil supply circuit 111 to which the discharge side of the hydraulic pump 110 is connected, whereas the port 105 is connected to the hydraulic oil discharge circuit 112 which is connected to the tank 107 of the hydraulic oil.
To the hydraulic oil supply circuit 111, a supply-side poppet valve 121 arranged to connect/disconnect the hydraulic cylinder 100 to/from the hydraulic pump 110, a flow rate control valve 123, and a supply-side stop valve 125 are connected. To the port 105, a discharge-side poppet valve 122, a flow rate control valve 124, and a discharge-side stop valve 126 are connected. Note that, in the figure the supply-side poppet valve 121 and the discharge-side poppet valve 122 take the cut-off positions at which the circuit is cut off, and the valves are switched to the connection positions after being operated.
In the hydraulic cylinder 100, as the supply-side poppet valve 121 is switched to the connection position while the discharge-side poppet valve 122 remains at the cut-off position (illustrated position), the ram 102 of the hydraulic cylinder 100 moves up on account of the working hydraulic oil supplied to the pressure chamber 103, as the hydraulic oil discharge circuit 112 is disconnected. To move down the ram 102 of the hydraulic cylinder 100, the discharge-side poppet valve 122 is switched to the connection position. The rate of move up of the ram 102 is controlled by the flow rate control valve 123, whereas the rate of move down is controlled by the flow rate control valve 124.
Flushing of the hydraulic oil supply circuit 111, the hydraulic oil discharge circuit 122, and the hydraulic cylinder 100 is carried out in such a way that, as both of the supply-side poppet valve 121 and the discharge-side poppet valve 122 are switched to the connection positions, a circulation circuit of the discharged hydraulic oil from the hydraulic pump 110 is formed to connect the hydraulic oil supply circuit 111 with the hydraulic oil discharge circuit 112 and the tank 107 via the hydraulic cylinder 100 and therefore the hydraulic oil circulates in this supply/discharge circuit.